Wide steel plates like those materials that are used in the body of automobiles are produced by major steelmaking companies in large quantities. A steelmaking company uses plural rolling mills aligned in tandem; steel sheet passes between wide mill rolls to be rolled by a large force of 1000 tons or more for reduction of its thickness. Such mass-production-oriented rolling mill employs, for efficient rolling, mostly a hydraulic screw-down apparatus consisting of a hydraulic servo control valve and a hydraulic jack as a means for generating a large roll force between the mill rolls. In recent years, in the fields of roll press machines for continuous roll-pressing of new materials and for rolling non-ferrous material to foil thinly, use of a hydraulic screw-down device that uses hydraulic pressure has increased for more enhanced plate thickness accuracy of the rolled material after rolling process.
When introducing the hydraulic screw-down device that uses hydraulic pressure into a small-size rolling mill, the roll-gap regulating movement of mill rolls has to be controlled finely; therefore, it is necessary to use a hydraulic servo control valve that is able to take in or put out a minute amount of oil. For a stable use of a hydraulic servo control valve, the oil temperature of the hydraulic pressure generating apparatus for supplying a high-pressure hydraulic pressure has to be maintained constant. It is, therefore, necessary to provide such a system that is required in a large rolling mill like a cooling water supply infrastructure for cooling the oil in the hydraulic tank. For simplifying a hydraulic screw-down system, apparatuses below-listed are disclosed.
Patent Literature 1 describes a plate thickness control. According to the description, the rod end of an intermediate cylinder is inserted in a main cylinder, and the plate thickness is controlled by raising or lowering the position of the ram of the main cylinder with hydraulically regulating the position of the rod of the intermediate cylinder.
Patent Literature 2 describes a configuration such that intermediate cylinders are provided and each of them is connected severally to each of both main cylinders incorporated in the driving side and the working side of a rolling mill, and two intermediate cylinders are connected by a rod. Further, a servo control valve is connected on one end of the intermediate cylinder to raise or lower the rams of the working side and the driving side of the main cylinder at the same speed.
Patent Literature 3 describes an ultrahigh-pressure generator that is configured with a movement-mechanism of threaded rod and spirality device, and hydraulic piston and cylinder.